The present invention is related to passenger detection systems, and in particular to passenger detection systems that classify an attribute of a passenger of an automobile in which an air bag device is installed.
Air bag devices ease the shock that a passenger experiences during an automobile collision. Air bags may be installed in front of the driver's and passenger's seats. Air bags may be installed in other locations, such as to the side of a passenger.
Many air bags are designed to deploy in front of the torso of an adult passenger seated in the seat. When a rear facing infant seat (hereafter RFIS) is located on the front passenger seat, it is desirable for the passenger-side air bag not to deploy. It may also be desirable for the air bag not to deploy for a forward facing child seat (hereafter “FFCS”), child or small adult. Likewise, deployment may be limited for side impact airbags based on whether a child or short person is leaning towards the air bag. Other reasons for preventing or limiting deployment (e.g. deploying with less force) may exist.
Passenger detection sensors have been proposed for detecting a RFIS, an FFCS or children. Systems using electric fields to detect characteristics of a load in a seat are disclosed in U.S. Pat. Nos. 5,948,031, 6,329,913, 6,329,914, 6,816,077 (Ser. No. 09/798,788, filed Mar. 2, 2001) and U.S. Pat. No. 6,696,948 (Ser. No. 10/033,585, filed Nov. 2, 2001). Other systems using capacitive sensing, such as systems to detect a change in phase or frequency due to the presence of a passenger, have also been proposed. Both types of systems rely on transmission and/or reception from one or more antennas or electrodes. Other passenger detection systems use ultrasound, infrared, light electromagnetic energy or other transmissions or receptions to detect one or more characteristics of occupants. Yet another type of detection system uses weight sensors, strain gauges, pattern recognition or other techniques or devices.
These occupant detection sensors are subjected to changing environmental conditions. Acceleration, deceleration, shocks from bumps or potholes or other factors may cause the sensor measurements or judgments to change frequently. The change is caused by a direct effect on the sensor or the shifting of an occupant's position in response to the changing conditions. As a result, the judgment and any indicators blink or change even though the detected occupant is the same. The sensor judgment may change even more frequently or in response to lesser changes in the environment for occupants close to judgment thresholds, such as a child just large enough to be classified as an adult or an adult small enough to be near the child threshold. Drivers may assume the changing judgment is associated with a faulty system and attempt to get the system fixed when nothing is wrong.
To avoid frequent changes in occupant detection based on changing environmental conditions, a five second hysteresis has been used. The final judgment or measurement conclusion changes only if five continuous seconds of measurements indicate the different judgment. However, some occupant movements or environmental conditions, such as extended turns on highway ramps or acceleration up a long hill, can continue for more than 5 seconds.